Method and apparatus for transmitting and receiving signal from relay station in radio communication system

ABSTRACT

A method of transmitting a signal, performed by a base station, in a wireless communication system. The method according to one embodiment includes transmitting a backhaul downlink signal to a relay station through a backhaul downlink transmission subframe. The backhaul downlink transmission subframe includes 14 orthogonal frequency division multiplexing (OFDM) symbols and the 14 OFDM symbols are indexed 0 to 13. An access downlink transmission subframe, used by the relay station to transmit a signal to a user equipment, and the backhaul downlink transmission subframe are transmitted with a time aligned subframe boundary, and OFDM symbols having indices K to 12 are used for transmitting the backhaul downlink signal, where K is a natural number and 1≦K≦5:

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. patent applicationSer. No. 14/044,577 filed on Oct. 2, 2013, which is a continuation ofU.S. patent application Ser. No. 13/201,805 filed Aug. 16, 2011 (nowU.S. Pat. No. 8,576,900, issued Nov. 5, 2013), which is the nationalphase of PCT International Application No. PCT/KR2010/000950 filed onFeb. 16, 2010, which claims priority to U.S. Provisional ApplicationNos. 61/152,951 filed on Feb. 16, 2009, 61/187,266 filed on Jun. 15,2009, 61/219,727 filed on Jun. 23, 2009, 61/236,162 filed on Aug. 24,2009, and 61/298,862 filed on Jan. 27, 2010, and which claims priorityto Korean Application No. 10-2010-0013907 filed on Feb. 16, 2010. Theentire contents of all of the above applications are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication, and moreparticularly, to a method of transmitting a signal in a wirelesscommunication system including a relay station.

2. Discussion of the Related Art

In ITU-R (International Telecommunication Union Radio communicationsector), a standardization task for IMT (International MobileTelecommunication)-Advanced (i.e., the next-generation mobilecommunication system after the 3^(rd) generation) is being in progress.IMT-Advanced sets its goal to support IP (Internet Protocol)-basedmultimedia service at the data transfer rate of 1 Gbps in the stop andslow-speed moving states and at the data transfer rate of 100 Mbps inthe fast-speed moving state.

3GPP (3^(rd) Generation Partnership Project) is a system standard tosatisfy the requirements of IMT-Advanced, and it is preparing forLTE-Advanced improved from LTE (Long Term Evolution) based on OFDMA(Orthogonal Frequency Division Multiple Access)/SC-FDMA (SingleCarrier-Frequency Division Multiple Access) transmission schemes.LTE-Advanced is one of the strong candidates for IMT-Advanced. Relaystation technology is included in the major technology of LTE-Advaneed.

A relay station is an apparatus for relaying signals between a basestation and a user equipment and is used to extend the cell coverage ofa wireless communication system and improve the throughput.

In a wireless communication system including a relay station, a lot ofresearches are being carried out on a method of transmitting a signalbetween a base station and the relay station. To use a conventionalmethod of transmitting a signal between a base station and a mobilestation in transmitting a signal between a base station and a relaystation without change is problematic.

In the conventional method of transmitting a signal between a basestation and a mobile station, in general, the mobile station transmits asignal over the one entire subframe when viewed from the time domain.One of the reasons why the mobile station transmits a signal over theone entire subframe is to set the duration time of each channel throughwhich the signal is transmitted as long as possible in order to reducethe maximum instant power consumed by the mobile station.

However, a relay station may not frequently transmit or receive a signalover the entire one subframe when viewed from the time domain. A relaystation experiences the frequent switching of a reception mode and atransmission mode because it relays signals for a plurality of mobilestations. There is a need for a specific time period (hereinafter calleda guard time) for which the relay station does not transmit or receive asignal in order to prevent interference between signals and stabilizethe operation between the reception mode period and the transmissionmode period when the reception mode and the transmission mode areswitched.

Unlike a mobile station, a relay station may not transmit or receive asignal over the one entire subframe owing to the guard time.Accordingly, the conventional method of transmitting a signal between abase station and a mobile station cannot be used without change.

Furthermore, since a relay station has fewer power restrictions ascompared with a mobile station and typically has an excellent channelstate with a base station, the conventional method of transmitting asignal between a base station and a mobile station needs not to be usedto transmit a signal between a base station and a relay station withoutchange.

There is a need for a new method of transmitting a signal in a wirelesscommunication system including a relay station.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method oftransmitting a signal in a wireless communication system including arelay station.

A method of a relay station transmitting and receiving a signal in awireless communication system, including the steps of receiving offsettime information from a base station; configuring a time differencebetween an access downlink transmission subframe through which an accessdownlink signal is transmitted to a relay user equipment and a backhauldownlink reception subframe through which a backhaul downlink signal isreceived from the base station based on the offset time information;transmitting a control signal to the relay user equipment through abackhaul downlink transmission subframe; and receiving the backhauldownlink signal from the base station through the backhaul downlinkreception subframe.

A signal can be efficiently transmitted in a wireless communicationsystem including a relay station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system including an RS.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

FIG. 3 is an exemplary diagram showing a resource grid for one downlinkslot.

FIG. 4 shows the structure of a downlink subframe.

FIG. 5 shows the structure of an uplink subframe.

FIG. 6 shows an operation which may be performed by an RS andrestriction conditions therefor.

FIGS. 7 and 8 show examples in which a guard time is disposed within asubframe.

FIG. 9 shows a propagation delay time and an offset time.

FIG. 10 shows an example of a timing relationship between the macrosubframe of a BS and the BDL Rx subframe and the ADL Tx subframe of anRS.

FIG. 11 shows another example of a timing relationship between the macrosubframe and the B-DL Tx subframe of a BS and the B-DL Rx subframe andthe A-DL Tx subframe of an RS.

FIGS. 12 to 14 show yet another example of a timing relationship betweenthe macro subframe and the B-DL Tx subframe of a BS and the B-DL Rxsubframe and the A-DL Tx subframe of an RS.

FIGS. 15 to 21 show examples of a timing relationship between a B-UL Txsubframe over which an RS transmits a backhaul UL signal to a BS and anA-UL Rx subframe over which an RS receives an access UL signal from anRe UE, on the basis of the macro subframe of the BS.

FIG. 22 shows an example of a timing relationship in a wirelesscommunication system including a BS, an RS, and an Re UE.

FIG. 23 shows another example of a timing relationship in a wirelesscommunication system including a BS, an RS, and an Re UE.

FIG. 24 shows yet another example of a timing relationship in a wirelesscommunication system including a BS, an RS, and an Re UE.

FIG. 25 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 26 and FIG. 27 show further yet another example of a timingrelationship in a wireless communication system including a BS, an RS,and an Re UE.

FIG. 28 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 29 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 30 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 31 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 32 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 33 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 34 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE,

FIG. 35 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UE.

FIG. 36 shows further yet another example of a timing relationship in awireless communication system including a BS, an RS, and an Re UX,

FIGS. 37 and 38 illustrate the symbol indices of B-UL Tx subframes overwhich a backhaul SRS is transmitted.

FIG. 39 is a block diagram showing a source station and a destinationstation.

DETAILED DESCRIPTION OF THE INVENTION

3GPP (3^(rd) Generation Partnership Project) LTE (Long Term Evolution)is part of an E-UMTS (Evolved-Universal Mobile TelecommunicationsSystem), and it adopts OFDMA (Orthogonal Frequency Division MultipleAccess) in downlink and adopts SC-FDMA (Single Carrier-FrequencyDivision Multiple Access) in uplink. LTE-A (LTE-Advanced) is theevolution of LTE. 3GPP LTE/LTE-A is chiefly described below, but thetechnical feature of the present invention is not limited thereto.

FIG. 1 shows a wireless communication system including a relay station.

Referring to FIG. 1, the wireless communication system 10 including arelay station includes at least one Base Station (BS) 11. The BS 11provides communication service to a specific geographical area 15commonly called a cell. The cell may be divided into a plurality ofareas. Each of the areas is called a sector. The one or more cells mayexist in one BS. In general, the BS refers to a fixed stationcommunicating with a User Equipment (UE) 13. The BS 11 may also hecalled another terminology, such as an eNB (evolved NodeB), a BTS (BaseTransceiver System), an access point, or an AN (Access Network). The BS11 may perform functions, such as connectivity between UEs 14,management, control, and resource allocation.

A Relay Station (RS) 12 refers to equipment for relaying a signalbetween the BS 11 and the UE 14, and it may also be called anotherterminology, such as a Relay Node (RN), a repeater, or a relay. Anymethod, such as AF (amplify and forward) and DF (decode and forward),may be used as a relay method used in the RS, and the technical featureof the present invention is not limited thereto.

The UE 13 or 14 may be fixed or mobile and may also be called anotherterminology, such as an MS (Mobile Station), an UT (User Terminal), anSS (Subscriber Station), a wireless device, a PDA (Personal DigitalAssistant), a wireless modem, a handheld device, or an AT (AccessTerminal. Hereinafter, a Macro UE (Ma UE) 13 refers to a UE directlycommunicating with the BS 11, and a relay UE (Re UE) 14 refers to a UEcommunicating with an RS. The Ma UE 13 placed within the cell of the BS11 may also communicate with the BS 11 via the RS 12 in order to improvethe transfer rate according to a diversity effect.

Hereinafter, a link between the BS 11 and the Ma UE 13 is said to be amacro link. The macro link may be divided into a macro downlink (M-DL)and a macro uplink (M-UL). The M-DL means communication from the BS 11to the Ma UE 13, and the M-UL means communication from the Ma UE 13 tothe BS 11.

A link between the BS 11 and the RS 12 is said to be a backhaul Thebackhaul link may be divided into a backhaul downlink (B-DL) and abackhaul uplink (B-UL). The B-DL means communication from the BS 11 tothe RS 12, and the B-UL means communication from the RS 12 to the BS 11.

A link between the RS 12 and the Re UE 14 is said to be an access link.The access link may be divided into an access downlink (A-DL) and anaccess uplink (A-UL). The A-DL means communication from the RS 12 to theRe UE 14, and the A-UL means communication from the Re UE 14 to the RS12,

The wireless communication system 10 including an RS is a systemsupporting bi-directional communication. The bi-directionalcommunication may he performed using a TDD (Time Division Duplex) mode,an FDD (Frequency Division Duplex) mode and the like. The TDD mode usedifferent time resources in UL transmission and DL transmission. The FDDmode uses different frequency resources in UL transmission and DLtransmission.

FIG. 2 shows the structure of a radio frame in 3GPP LTE.

Referring to FIG. 2, the radio frame includes 10 subframes. One subframeconsists of two slots. The time taken to transmit one subframe is calleda TTI (Transmission Time Interval). For example, the length of onesubframe may be 1 millisecond(ms) and the length of one slot may be 0.5ms.

For the structure of the radio frame described with reference to FIG. 2,reference can be made to Section 4.1 and Section 4.2 of 3GPP TS 36.211V8.3.0 (2008 May) “Technical Specification Group Radio Access Network;Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channelsand Modulation (Release 8)”.

FIG. 3 is an exemplary diagram showing a resource grid for one downlinkslot.

In FDD and TDD radio frames, one slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand includes a plurality of resource blocks (RB) in the frequencydomain. The OFDM symbol is for representing one symbol period (or symboltime) because 3GPP LTE uses OFDMA in downlink. The OFDM symbol may alsobe called an SC-FDMA symbol according to multiple access scheme. Thesymbol period may hereinafter refer to one OFDM symbol or one SC-FDMAsymbol. The resource block is a resource allocation unit, and itincludes plurality of consecutive subcarriers in one slot.

Referring to FIG. 3, a slot (e.g., a downlink slot included in adownlink subframe) includes a plurality of OFDM symbols in the timedomain. Here, the one downlink slot is illustrated to include 7 OFDMsymbols and one resource block is illustrated include 12 subcarriers inthe frequency domain, but not limited thereto.

Each element on the resource grid is called a resource element. Oneresource block includes 12×7 resource elements. The number of resourceblocks N^(DL) included in the downlink slot is dependent on a DLtransmission bandwidth configuration in a cell.

FIG. 4 shows the structure of a downlink subframe.

Referring to FIG. 4, the subframe includes 2 consecutive slots. Thefirst 3 OFDM symbols in the first slot of the subframe correspond to acontrol region to which PDCCH(physical downlink control channels areallocated, and the remaining OFDM symbols correspond to a data region towhich PDSCH(physical downlink shared channels are allocated. Controlchannels, such as PCFICH(physical control format indicator channel) andPHICH(physical hybrid automatic repeat request indicator channel), maybe allocated to the control region in addition to the PDCCHs. A UE canread data information transmitted through the PDSCH by decoding controlinformation transmitted through the PDCCH. The control region isillustrated to include the 3 OFDM symbols, but is only exemplary. 2 OFDMsymbol or 1 OFDM symbol may be included in the control region. Thenumber of OFDM symbols included in the control region within thesubframe can be known through the PCFICH.

The control region is formed of a logical CCE column including aplurality of CCEs (control channel elements). The CCE column is a set ofall CCEs which form the control region within one subframe. The CCEcorresponds to a plurality of resource element groups. For example, TheCCE may correspond to 9 resource element groups. The resource elementgroup is used to define that the control channel is mapped to theresource element. One resource element group may consist of 4 resourceelements.

A plurality of PDCCHs may be transmitted within the control region. ThePDCCH carries control information, such as scheduling allocation. ThePDCCH is transmitted over one CCE or an aggregation of severalconsecutive CCEs. The format of the PDCCH and the number of possiblebits of the PDCCH are determined according to the number of CCEs formingthe CCE aggregation. The number of CCEs used for PDCCH transmission iscalled a CCE aggregation level. Furthermore, the CCE aggregation levelis a CCE unit for searching for a PDCCH. The size of the CCE aggregationlevel is defined by the number of contiguous CCEs. For example, the CCEaggregation level may be an element of {1, 2.4. 8}.

The control information transmitting through the PDCCH is calledDownlink Control Information (hereinafter DCI). The DCI includes ULscheduling information, DL scheduling information, system information,UL power control command, control information for paging, controlinformation for a random access response (RACH response) and the like.

The DCI format includes a format 0 for PUSCH (Physical Uplink SharedChannel) scheduling, a format 1 for the scheduling of one PDSCHcodeword, a format 1A for the compact scheduling of one PDSCH codeword,a format 1B for compact scheduling for the rank-1 transmission of asingle codeword in a spatial multiplexing mode, a format 1C for the verycompact scheduling of a DL-SCH (Downlink Shared Channel), a format 1Dfor PDSCH scheduling in a multiple user spatial multiplexing mode, aformat 2 for PDSCH scheduling in a closed-loop spatial multiplexingmode, a format 2A for PDSCH scheduling in an open-loop spatialmultiplexing mode, a format 3 for the transmission of the TPC(Transmission Power Control) command of 2-bit power control for aPUCCH(physical uplink control channel) and a PUSCH, a format 3A for thetransmission of the TPC command of 1-bit power control for a PUCCH and aPUSCH and the like.

FIG. 5 shows the structure of an uplink subframe.

Referring to FIG. 5, the uplink subframe may be divided into a controlregion to which a PUCCH for carrying UL control information is allocatedand a data region to which a PUSCH for carrying user data is allocatedin the frequency domain.

A pair of resource blocks (RB) 51 and 52 is allocated to the PUCCH forone UE in the subframe. The pair of RBs 51 and 52 occupy differentsubcarriers in two slots, respectively. This is said that the RB pairallocated to the PUCCH is subjected to frequency hopping at a slotboundary.

The PUCCH can support multiple formats. That is, the PUCCH transmit ULcontrol information having a different number of bits per subframeaccording to a modulation scheme. For example, when BPSK (Binary PhaseShift Keying) is used (PUCCH format 1a), the UL control information of 1bit can be transmitted through the PUCCH. When QPSK (Quadrature PhaseShift Keying) is used (PUCCH format 1b), the UL control information of 2bits can be transmitted through the PUCCH. The PUCCH format may includea format 1, a format 2, a format 2a, a format 2b and the like (For this,reference can be made to Section 5.4 of 3GPP TS 36.211 V8.2.0 (2008March) “Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)”).

FIG. 6 shows an operation which may be performed by an RS andrestriction conditions therefor.

The RS can perform backhaul uplink transmission (B-UL Tx) and backhauldownlink reception (B-DL Rx) in a relationship with a BS. The BS canperform backhaul downlink transmission (B-DL Tx) and backhaul uplinkreception (B-UL Rx) in a relationship with the RS.

The RS can perform access downlink transmission (A-DL Tx) and accessuplink reception (A-UL Rx) in a relationship with an Re UE. The Re UEcan perform access uplink transmission (A-UL Tx) and access downlinkreception (A-DL Rx) in a relationship with the RS.

Although not shown in FIG. 6, the BS can perform macro downlinktransmission (M-DL Tx) and macro uplink reception (M-UL Rx) in arelationship with an Ma UE.

In general, an RS cannot transmit and receive signals at the same timein the same frequency band owing to self-interference. That is, the RScannot perform B-DL Rx and A-DL Tx at the same time. Furthermore, the RScannot perform B-UL Tx and A-UL Rx at the same time. Accordingly, thetransmission and reception of signals in the same frequency band areperformed over different subframes.

in general, when B-DL Rx and A-DL Tx are switched, the RS requires aguard time (or guard period). Likewise, when B-UL Tx and A-UL Rx areswitched, the RS requires a guard time. The guard time may be about 20microsecond(μs) by taking the transient time characteristic of an analogamplifier, used in the RS, into consideration.

FIGS. 7 and 8 show examples in which a guard time is disposed within asubframe.

The guard time may be time duration smaller than one symbol (e.g., oneOFDM symbol or one SC-FDMA symbol). That is, in the temporal aspect, theguard time may be part of one symbol. The position of the guard time andthe size of the guard time may be changed in various ways according tothe structure of a backhaul subframe and a timing relationship betweenaccess subframes. For example, one of the guard times may be placed atthe central symbol of a subframe as shown in FIG. 7, or the guard timesmay be placed at the first and the last symbols of a subframe as shownin FIG. 8. In 3GPP LTE, a minimum scheduling unit is a subframe.Accordingly, if transmission reception switching is performed in abackhaul link and an access link, an RS performs the switching by theunit of subframe. In this case, the guard times are placed at the firstsymbol and the last symbol of a subframe as shown in FIG. 8. If theguard time is placed within one symbol, although the guard time occupiesa time period smaller than one symbol, the related symbol may not beused (parts of symbols that cannot be used in FIGS. 7 and 8 areindicated by ‘N’). That is, the symbol including the guard time iswasted.

Furthermore, in 3GPP LTE, an SRS (sounding reference signal) for ULscheduling is transmitted over the last symbol of a subframe. If thelast symbol of a subframe cannot be used owing to the guard time asdescribed above, an RS is difficult to transmit the SRS.

One of methods for solving the problem is a method of defining a newsymbol. In other words, a symbol, having a time period smaller than thatof a conventional symbol (e.g., an OFDM symbol or an SC-FDMA symbol), isdefined. The waste of radio resources can be prevented by applying thenew symbol to the time duration which is wasted owing to a guard time.

Another method for solving the above problem is to shift a signaltransmission/reception subframe between a BS, an RS, and a UE based onoffset time information or additional alignment information or both.

Terms are first defined, for clarity of description.

FIG. 9 shows a propagation delay time and an offset time.

Referring to FIG. 9( a), a BS performs B-DL TX. In this case, an RSperforms B-DL Rx after a propagation delay time Tp. That is, thepropagation delay time is the delay time occurring owing to thetransmission of a physical signal, in the time taken for a sourcestation to transmit a signal and the time taken for a destinationstation to receive the signal. An offset time To means an intentionaloffset between the backhaul link subframe and the access link subframeof the RS. In FIG. 9( a), the RS may perform B-DL Rx and A-DL Tx withthe offset time To. The information for propagation delay time or theoffset time or both can be transmitted from a BS to an RS and a UE. TheBS may transmit information for the offset time through thesynchronization signal of a P-BCH or a physical channel (e.g., a PDCCH).When the information for offset time is received from the BS, the RS orthe UE transmits or receive a signal in response to relevant timing.

FIG. 9( b) is a diagram except the propagation delay time of FIG. 9( a).If the propagation delay time is excluded, FIG. 9( a) can be simplyshown as in FIG. 9( b). In the following description and figures, thepropagation delay time is excluded, if necessary, and a timingrelationship for signal transmission reception between a BS, an RS, anda UE is shown.

FIGS. 10 to 14 are diagrams showing timing relationships between asubframe over which an RN receives a backhaul DL signal from an eNB anda subframe over which the RN transmits an access DL signal to an Re UEon the basis of a macro subframe. Here, the propagation delay time istaken into account.

FIG. 10 shows an example of a timing relationship between the macrosubframe of an eNB and the B-DL Rx subframe and the A-DL Tx subframe ofan RN.

Referring to FIG. 10, the macro subframe and the B-DL Tx subframe a ealigned. The B-DL Rx subframe is temporally placed behind the B-DL Txsubframe by a propagation delay time Tp by taking the propagation delaytime Tp into account. The A-DL Tx subframe is shifted by a fixed offsettime To and placed in the B-DL Rx subframe. It corresponds to a casewhere a switching time in the RN is longer than a cyclic prefix.

In this timing relationship, it is assumed that the RN transmits acontrol signal to the Re UE using K symbols. For example, it is assumedthat the number of symbols used in an R-PDCCH through which the RNtransmits the control signal to the Re UE is K (the same hereinafter).In this case, the RN can receive a backhaul DL signal over symbolshaving a symbol index M=K+1 to the last symbol index of the subframe.For example, assuming that the number of symbols used in the R-PDCCHtransmitted by the RN is 2, the RN can receive the backhaul DL signalusing symbols from a symbol index 3 to a symbol index 13 (i.e., the lastsymbol of the subframe. There is an advantage in that available radioresources in a backhaul link are increased because the RN can use thesymbol having the symbol index 3 and the symbol having the symbol index13.

FIG. 11 shows another example of a timing relationship between the macrosubframe and the B-DL Tx subframe of an eNB and the B-DL Rx subframe andthe A-DL Tx subframe of an RN.

This timing relationship corresponds to a case where the switching timeof the RN is very short (e.g., shorter than a cyclic prefix) and a casewhere the B-DL Rx subframe and the A-DL Tx subframe are aligned. Theswitching time may he very short according to the performance of ananalog amplifier used in the RN. Here, the guard time is placed ahead ofa symbol having a symbol index 2 in the B-DL Rx subframe and placedbehind a symbol having a symbol index 13. Since the time period of theguard time is shorter than the cyclic prefix, it may be said thatsynchronization between symbols is not influenced.

In this timing relationship, the RN can receive a backhaul DL signalusing symbols from a symbol index M=K to the last symbol index of thesubframe. That is, this timing relationship differs from that of FIG. 10in that the symbol index at which the backhaul DL signal can be receivedis started from K.

FIGS. 12 to 14 show yet another example of a timing relationship betweenthe macro subframe and the B-DL Tx subframe of an eNB and the B-DL. Rxsubframe and the A-DL Tx subframe of an RN.

Referring to FIG. 12, the B-DL Tx subframe of the eNB and the A-DL Txsubframe of the RN are started on the same time (i.e., synchronized).The B-DL Rx subframe may be shifted from the B-DL Tx subframe by apropagation delay time Tp. This timing relationship corresponds to acase where the propagation delay time To is shorter than one symbolperiod L, the propagation delay time Tp is shorter than a guard time G1,and a (Tp+guard time G2) is shorter than a symbol period L. This may herepresented by [(Tp<L) & (Tp<G1) & (Tp+G2<L), the symbol period=L].

The RN can receive a backhaul DL signal from a symbol having a symbolindex M(K or higher than K) to a symbol having a symbol index of n. Thesymbol index n may be varied according to the propagation delay time Tpand the size of a guard time according to a switching time. For example,when K=2, in FIG. 12, the RN can receive the backhaul DL signal usingsymbols having symbol indices M=3 to 12.

FIG. 13 shows an example in which a guard time G1 is shorter than apropagation delay time Tp, the propagation delay time Tp is shorter thana symbol period L, and the sum of the propagation delay time Tp and aguard time G2 is shorter than the symbol period L. That is, [(G1<Tp<L) &(Tp÷G2<L), the symbol period=L]. In this case, the RN can receive abackhaul DL signal using symbols having symbol indices M=2 to 12. Thatis, the RN can use the 11 symbols for backhaul downlink reception(B-DLRx).

FIG. 14 shows an example in which a guard time G1 is shorter than apropagation delay time Tp, the propagation delay time Tp is shorter thana symbol period L, and the sum of the propagation delay time Tp and aguard time G2 is greater than the symbol period L. That is, [(G1<Tp<L) &(Tp+G2>L), the symbol period=L]. In this case, an RN can receive abackhaul DL signal using symbols having symbol indices M=2 to 11. Thatis, the RN can use the 10 symbols for B-DL Rx.

FIGS. 15 to 21 show examples of a timing relationship between a B-UL Txsubframe over which an RN transmits a backhaul UL signal to an eNB andan A-UL Rx subframe over which an RN receives an access UL signal froman Re UE, on the basis of the macro subframe of the eNB. Here, thepropagation delay time is taken into account.

In FIG. 15, the B-UL Tx subframe and the A-UL Rx subframe have a timedifference of a fixed offset value. FIG. 15 shows the example in whichthe offset time To has a negative value. The RN can puncture a symbolhaving an SC-FDMA symbol index of 0 and transmit the backhaul UL signalusing 13 symbols having an SC-FDMA symbol index 1 to an SC-FDMA symbolindex 13 (in case of a normal CP). That is, the offset time is placedbetween the B-UL Tx subframe over which the RN transmits the backhaul ULsignal and the A-UL Rx subframe over which the RN receives the access ULsignal from the Re UE, so that the RN can use the 13 symbols to transmitthe backhaul UL signal.

In FIG. 16, there is no time difference between the B-UL Tx subframe andthe A-UL Rx subframe of an RN. That is, an offset value does not exist.This timing relationship corresponds to a case where the B-UL Txsubframe and the A-UL Rx subframe of the RN are aligned and theswitching time of the RN is very short (e.g., a case where the switchingtime is shorter than a cyclic prefix). When the switching time of the RNis very short, there is no problem although the guard time is veryshort. Accordingly, the guard time necessary to switch the backhaul ULTx and the access UL Rx of the RN rarely has an influence on thesubframe structure. The RN can transmit the backhaul UL signal using 14symbols having SC-FDMA symbol indices 0 to 13.

In FIG. 17, a time difference having a fixed offset value is placedbetween the B-UL Tx subframe and the A-UL Rx subframe of an RN. FIG. 17shows an example in which the offset time has a negative value. FIG. 17differs from FIG. 16 in that a guard time necessary between the A-UL Rxsubframe and the B-UL Tx subframe of the RN is placed in the A-UL Rxsubframe. Accordingly, the RN can transmit a backhaul UL signal usingall 14 symbols having SC-FDMA symbol indices 0 to 13 (in case of anormal CP). Meanwhile, since the guard time is placed at the last symbolof the AWL Rx subframe, the Re UE may be difficult to transmit an SRSover the last symbol. This is because the RN is difficult to receive theSRS.

In FIG. 18, a time difference of a fixed offset value is placed betweenthe B-UL Tx subframe and the A-UL Rx subframe of an RN. FIG. 18 isdifferent from FIG. 17 in that the offset time has a positive value.That is, the A-UL Rx subframe is temporally ahead of the B-UL Txsubframe by the offset time. In this timing relationship, the RN cantransmit a backhaul UL signal using 13 symbols having SC-FDMA symbolindices 0 to 12 (in case of a normal CP). The last symbol (i.e., asymbol having a symbol index 13) of the B-UL Tx subframe cannot be usedowing to a guard time.

In FIG. 19, the A-UL Rx subframe of an RN and the B-UL Rx subframe of aneNB are aligned, and a B-UL Tx subframe is placed by taking apropagation delay time into account. This timing relationship may beapplied to a case where the sum of a propagation delay time Tp and aguard time G1 is smaller than one symbol period L, the propagation delaytime Tp is smaller than the guard time G1, and the sum of thepropagation delay time Tp and the symbol period L is greater than aguard time G2. That is, the timing relationship may be applied to[(Tp+G1<L) & (Tp<G1) & (Tp+L>G2), the symbol period=L].

The RN can transmit a backhaul UL signal during a period from a symbolhaving a symbol index N of 1 or higher to a symbol having a symbol indexN of 12 over the B-UL Tx subframe (in case of a normal CP). That is, theRN can transmit the backhaul UL signal over the 12 symbols.

Like in FIG. 19, in FIG. 20, the A-UL Rx subframe of an RN and the B-ULRx subframe of an eNB are aligned, and a B-UL Tx subframe is placed bytaking a propagation delay time into account. FIG. 20 differs from FIG.19 in an application condition. The timing relationship, such as thatshown in FIG. 20, may be applied to a case where the sum of apropagation delay time Tp and a guard time G1 is smaller than one symbolperiod L, a guard time G2 is smaller than the propagation delay time Tp,and the propagation delay time Tp is smaller than the symbol period L.That is, the timing relationship may be applied to [(Tp+G1)<L &(G2<Tp<L), the symbol period=L]. The RN can transmit a backhaul ULsignal using a period from a symbol having a symbol index N of 1 to asymbol having a symbol index N of 13 (in case of a normal CP). That is,the RN can transmit the backhaul UL signal using the 13 symbols.

Like in FIG. 20, in FIG. 21, the A-UL Rx subframe of an RN and the B-UL.Rx subframe of an eNB are aligned, and a B-UL Tx subframe is placed bytaking a propagation delay time into account. The application conditionin which the timing relationship of FIG. 21 is applied is a case wherethe sum of a propagation delay time Tp and a guard time G1 is greaterthan one symbol period L, a guard time G2 is smaller than thepropagation delay time Tp, and the propagation delay time Tp is smallerthan the symbol period L. That is. [(Tp+G1>L) & (G2<Tp<L), the symbolperiod=L]. The RN can transmit a backhaul UL signal using 12 symbolshaving symbol indices N of 2 to 13 (in case of a normal CP).

How each of an eNB, an RN, and an Re UE is operated according to whattiming relationship is described below in a wireless communicationsystem including the eNB, the RN, and the Re UE.

FIG. 22 shows an example of a timing relationship in a wirelesscommunication system including an eNB, an RN, and an Re UE. Apropagation delay time is not shown in FIG. 22.

Referring to FIG. 22, the starting positions of subframe aresynchronized between the eNB and the RN or between the eNB and the UE.In a subframe #(n+1), the RN receives (A-UL Rx) an access UL signaltransmitted by the UE and transmits (B-UL Tx) a backhaul UL signal overa subframe #(n+2). The RN cannot transmit the backhaul UL signal becausea guard time is placed within the subframe, as shown in FIG. 22, whenthe RN transmits (B-UL Tx) the backhaul UL signal over the subframe#(n+2) or a subframe #n. The RN transmits the backhaul UL signal using ashortened format (i.e., the first symbol and the last symbol from among14 symbols included in the subframe are punctured and only 12 symbolsare used). If the backhaul UL signal is transmitted using the shortenedformat, in order to transmit a backhaul SRS (indicated by S′), the RNhas to transmit the SRS of a special form. That is, the RN generates theSRS of a special form, defined for a period smaller than one symbol, andtransmits the backhaul SRS over the last symbol of the subframe.

FIG. 23 shows another example of a timing relationship in a wirelesscommunication system including an eNB, an RN, and an Re UE. Apropagation delay time is not shown in FIG. 23.

Referring to FIG. 23, an offset having a fixed time exists in the timingrelationship between the subframes of the eNB and the RN and in thetiming relationship between the subframes of the RN and the UE. In asubframe μ(n+1), the A-DL Tx subframe and the A-UL Rx subframe of theRN, and the A-DL Rx subframe and the A-UL Tx subframe of the UL areforwardly shifted by an offset time To on the basis of an M-DL Txsubframe and an M-UL Rx subframe which are macro subframes. As describedabove, the offset time To is a value given by the eNB and may bedetermined according to the structure of a subframe used in the backhaul

When the wireless communication system is operated according to thetiming relationship, the RN can transmit a backhaul UL signal using 13symbols (in case of a normal CP). That is, the method described abovewith reference to FIG. 18 may be applied to the timing relationship.

Furthermore, the RN can receive a backhaul DL signal using 10 or 11symbols (in case of a normal CP). That is, any one of the methodsdescribed above with reference to FIGS. 12 to 14 may be applied to thetiming relationship.

FIG. 24 shows yet another example of a timing relationship in a wirelesscommunication system including an eNB, an RN, and an UE. A propagationdelay time is not shown in FIG. 24.

Referring to FIG. 24, an offset having a fixed time exists in the timingrelationship between the subframes of the eNB and the RN and the timingrelationship between the subframes of the RN and the UE. In a subframe#(n+1), the A-DL Tx subframe and the A-UL Rx subframe of the RN and theA-DL Rx subframe and the A-UL Tx subframe of the UE are backwardlyshifted by an offset time To on the basis of an M-DL Tx subframe and anM-UL Rx subframe which are macro subframes. This is different from FIG.23. As described above, the offset time To is a value given by the eNBand may be determined according to the structure of a subframe used inthe backhaul link.

When the wireless communication system is operated according to thistiming relationship, the RN can transmit a backhaul UL signal using 13symbols (in case of a normal CP). The method described above withreference to FIG. 15 may be applied to the timing relationship. FIG. 24is different from FIG. 23 in that the RN can use the last symbol of theB-UL Tx subframe over which the backhaul UL signal is transmitted andthe B-UL Tx subframe is synchronized with a macro subframe for eachsymbol. Accordingly, there is an advantage in that a backhaul SRS(indicated by S′) can be multiplexed with an SRS transmitted by an Ma UEand then transmitted. Alternatively, the RN may transmit the backhaul ULsignal using all 14 symbols (in case of a normal CP). That is, themethod described with reference to FIG. 17 may be applied to the timingrelationship. If the method described with reference to FIG. 17 isapplied, the RN does not receive an access UL signal over the lastsymbol of the A-UL Rx subframe, but places a guard time G1 in the lastsymbol of the A-UL Rx.

Furthermore, if the number of symbols used in an R-PDCCH transmitted tothe UE is K, the RN can receive a backhaul DL signal using symbolshaving a symbol index K+1 to the last index. That is, the methoddescribed above with reference to FIG. 10 may be applied to this timingrelationship.

FIG. 25 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an UE. Apropagation delay time is not shown in FIG. 25.

Referring to FIG. 25, the macro subframes (i.e., M-DL Tx subframe and anM-UL Rx subframe) of the eNB are misaligned. The access subframes i.e.,an A-DL Tx subframe and an A-UL Rx subframe) of the RN are aligned. Theaccess subframe of the RN is shifted from the backhaul subframe of theRN by an offset time To. That is, the access subframe of the RN istemporally ahead of the backhaul subframe of the RN by the offset timeTo. Because of the offset time, the RN can transmit a backhaul UL signalusing the 13 symbols of the B-UL Tx subframe (in case of a normal CP).Furthermore, if the RN transmits a backhaul SRS (indicated by S’) overthe B-UL Tx subframe, there is an advantage in that the symbol issynchronized with a symbol through which an Ma UE transmits an SRS bysymbol unit.

FIG. 26 and FIG. 27 show further yet another example of a timingrelationship in a wireless communication system including an eNB, an RN,and an UE. A propagation delay time is not shown in FIGS. 26 and 27.

As shown in FIGS. 26 and 27, the eNB may forwardly shift an M-UL. Rxsubframe so that it is synchronized with a B-UL Rx subframe for eachsymbol unit. The B-DL Tx subframe of the eNB and the B-DL Rx subframe ofthe RN are synchronized with each other. Likewise, the B-UL Rx subframeof the eNB and the B-UL Tx subframe of the RN are synchronized with eachother. In the RN, access subframes (i.e., an A-DL Tx subframe and anA-UL Rx subframe) are synchronized with each other.

An M-UL Rx subframe and the B-UL Rx subframe can be synchronized witheach other for each symbol according to this timing relationship.Accordingly, there is an advantage in that the RN does not need totransmit a special SRS in which a backhaul SRS is placed in the timedomain smaller than one symbol. If the synchronization is performed foreach symbol, interference between an SRS transmitted by an Ma UE and thebackhaul SRS transmitted by the RN is reduced. FIG. 27 is different fromFIG. 26 in that a guard time is indicated in another period.

FIG. 28 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an UE. Apropagation delay time is not shown in FIG. 28.

Referring to FIG. 28, all the macro subframe and the backhaul subframeof the eNB, the backhaul subframe and the access subframe of the RN, andthe access subframes of the UE are aligned and synchronized with eachother.

In this timing relationship, the eNB wastes 2 symbols owing to a guardtime in a B-DL Tx subframe, and the RN also wastes 2 symbols owing to aguard time in a B-DL Rx subframe. The same is true of the B-UL Rxsubframe of the eNB and the B-UL Tx subframe of the RN. In the symbolsincluding the guard time, a part indicated by ‘U’ is the wasted region.If some of the symbols are referred to as partial symbols, the wasteproblem of the partial symbols can be solved by defining and using a newsymbol as described above.

FIG. 29 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an UE. Apropagation delay time is taken into account and shown in FIG. 29.

Hereinafter, a round trip delay time between the eNB and the RN isindicated by RTD_(eNB-RS), and a round trip delay time between the RNand the UE is indicated by RTD_(RS-UE). The propagation delay time maybe (RTD_(eNB-RS)/2) between the eNB and the RN and may be(RTD_(RS-UE)/2) between the RN and the UE.

Referring to FIG. 29, the B-UL Rx subframe of the eNB is aligned with anM-UL Rx subframe. The B-UL Tx subframe of the RN may be placed ahead ofthe B-UL Rx subframe of the eNB by (RTD_(eNB-RS)/2) by taking thepropagation delay time into account. Furthermore, the B-DL Rx subframeof the RN may be placed behind the B-DL Tx subframe of the eNB by(RTD_(eNB-RS)/2). In this case, the B-UL Tx subframe and the B-DL Rxsubframe of the RN may be placed with a difference by RTD_(eNB-RS). Thatis, the backhaul link subframes i.e., the B-UL Tx subframe and the B-DLRx subframe) of the RN are misaligned. In the RN, the B-DL Rx subframeand the A-DL Tx subframe are switched and used, and the B-UL Tx subframeand the A-UL Rx subframe are switched and used. The A-DL Tx subframe andthe A-UL Rx subframe of the RN have also to be placed with a differenceby RTD_(eNB-RS) by taking the above into account.

When a relationship between the RN and the UE is taken into account, incase of A-UL, the UE has only to transmit an access UL signal ahead of(RTD_(RS-UE)/ 2) by taking the propagation delay time intoconsideration. That is, the A-UL Tx subframe of the UE has only to beplaced ahead of the A-UL Rx subframe of the RN by (RTD_(RS-UE)/2). Incase of access downlink(A-DL), the A-DL Tx subframe of the RN has onlyto be placed ahead of the A-DL Rx subframe of the UE by (RTD_(RS-UE)/2).However, since there is the difference of RTD_(eNB-RS) between the A-DLTx subframe and the A-UL Rx subframe of the RN, the A-UL Tx subframe andthe A-DL Rx subframe of the UE should not be placed with the differenceof RTD_(RS-UE), but have to be placed with a difference of(RTD_(eNB-RS)+RTD_(RS-UE)).

According to this timing relationship, when a legacy UE (e.g., a UEoperated according to 3GPP LTE release 8) attempts initial access owingto a reason, such as the entry of a cell), the legacy UE transmits aPRACH(physical random access channel) preamble like in a conventionalmethod used in a relationship with an eNB because it does not knowwhether a destination station is the eNB or an RN. There may be adisadvantage in that the legacy UE has to transmit a preamble having alarge coverage when the RN has a small cell size. However, there is anadvantage in that radio resources useful for the RN to transmit abackhaul UL signal can be maximized.

FIG. 30 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an UE. Apropagation delay time is taken into account and shown in FIG. 30.

Referring to FIG. 30, downlink subframes (i.e., a B-DL Rx subframe andan A-DL Tx subframe) and uplink subframes B-UL Tx subframe and an A-UL.Rx subframe) are aligned in the RN. The B-UL, Tx subframe and the B-DLRx subframe of the RN may be placed behind the B-UL Rx subframe and theB-DL Tx subframe of the eNB by (RTD_(eNB-RS)/2).

This timing relationship does not have an influence on a legacy UE(e.g., a UE operated according to 3GPP LTE release 8). Resources thatmay be used by the RN in backhaul UL transmission are reduced byRTD_(eNB-RS) in the time domain, but there is an advantage in that thelegacy UE can be operated by applying the same time difference betweenan A-DL Rx subframe and an A-UL Tx subframe. Furthermore, ifRTD_(eNB-RS) is greater than a guard time, the RN may multiplex abackhaul SRS with an SRS transmitted by an Ma UE and then transmit themultiplexed SRS.

Timing relationships in which an eNB, an RN, and a UE transmit andreceive signals for each symbol of a subframe are described below. Inthe following figures, a part indicated by ‘G’ means a guard time, ‘S’means an SRS transmitted from the UE to the eNB, and ‘S′’ means abackhaul SRS transmitted from the RN to the eNB. A propagation delaytime is not shown.

FIG. 31 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

Referring to FIG. 31, an M-UL Rx subframe, an M-DL Tx subframe, a B-DLRx subframe, a B-UL Tx subframe, an A-DL Rx subframe, and A-UL Txsubframes are aligned on the basis of a subframe boundary. The B-DL Rxsubframe and the B-UL Tx subframe are aligned on the basis of thesubframe boundary, but include guard times. Accordingly, the B-DL Rxsubframe and the B-UL Tx subframe are not aligned for each symbol. Theguard time included in the B-DL Rx subframe may be included in adifferent symbol from that of FIG. 31, and the start point of a symbolat which a backhaul DL signal is received from the eNB over the B-UL Txsubframe may be different form that of FIG. 31.

FIG. 32 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

Referring to FIG. 32, a B-DL Rx subframe, a B-UL Tx subframe, an A-DL Rxsubframe, and an A-UL Tx subframes have different points of timing basedon a subframe boundary in regard to an M-UL Rx subframe and an M-DL Txsubframe. That is, the B-DL Rx subframe and the B-UL Tx subframe of theRN and the A-DL Rx subframe and the A-UL Tx subframe of the Re UE have anegative offset time. The eNB can transmit information about the offsettime so that the RN and the Re UE have a timing relationship. A symbolthrough which a backhaul SRS is transmitted, in the B-UL Tx subframe, isaligned with a symbol through which a macro SRS is received over theM-UL Rx subframe by symbol unit.

FIG. 33 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

Unlike in FIG. 32, in FIG. 33, the B-DL Rx subframe and the B-UL Txsubframe of the RN and the A-DL Rx subframe and the A-UL Tx subframe ofthe Re UE have a positive timing offset in regard to an M-UL Rx subframeand an M-DL Tx subframe. A backhaul SRS transmitted over the B-UL Txsubframe may be transmitted over a different symbol (the thirteenthsymbol of the B-UL Tx subframe) from a macro SRS a macro SRS receivedover the M-UL Rx subframe) transmitted by an Ma UE. Accordingly, themacro SRS and the backhaul SRS need not to be multiplexed in the lastsymbol (a fourteenth symbol) of the subframe.

FIG. 34 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

Referring to FIG. 34, an M-DL Tx subframe, a Rx subframe, and an A-DL Rxsubframe are aligned on the basis of a subframe boundary. That is, in amacro subframe, a backhaul subframe, and an access subframe, downlinksubframes are aligned on the basis of the subframe boundary. On theother hand, in regard or an M-UL Rx subframe, a B-UL Tx subframe and anA-UL Tx subframe misaligned on the basis of the subframe boundary. TheeNB can apply this timing relationship by transmitting an additionaltiming adjustment command (indicated by TA′) to the RN or the UE. Here,the additional timing adjustment command may be a signal which isadditionally transmitted in addition to the existing timing adjustmentcommand in order to compensate for a propagation delay time or a roundtrip time.

This timing relationship cannot be applied to the existing legacy UEbecause it does not understand the additional timing adjustment command,but can be applied to a UE which can understand the additional timingadjustment command TA′. FIG. 34 shows an example in which the additionaltiming adjustment command TA′ having a negative value is performed. Thatis, FIG. 34 shows an example in which the B-UL Tx subframe and the A-ULTx subframe are temporally shifted backwardly. In this timingrelationship, a backhaul SRS and a macro SRS transmitted over the B-ULTx subframe can be aligned for each symbol.

FIG. 35 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

Like in FIG. 34, in FIG. 35, an M-DL Tx subframe, a B-DL Rx subframe,and an A-DL Rx subframe are aligned on the basis of a subframe boundary.On the other hand, an M-UL Rx subframe, a B-UL Tx subframe, and an A-ULTx subframe are misaligned on the basis of the subframe boundary. FIG.35 is different from FIG. 34 in that an additional timing adjustmentcommand is set to a positive value. That is, FIG. 35 shows an example inwhich the B-UL Tx subframe and the A-UL Tx subframe are temporallyshifted forwardly.

FIG. 36 shows further yet another example of a timing relationship in awireless communication system including an eNB, an RN, and an Re UE.

An M-DL Tx subframe, a B-DL Rx subframe, and an A-DL Rx subframe arealigned on the basis of a subframe boundary. An additional timingadjustment command having a positive value is applied to an M-UL Rxsubframe, a B-UL Tx subframe, and an A-UL Tx subframe. FIG. 36 differsfrom FIG. 35 in that the degree that the B-UL Tx subframe and the A-UL.Tx subframe are shifted is one symbol or more. For example, the B-UL Txsubframe and the A-UL Tx subframe may be forwardly shifted by (onesymbol+a guard time). The B-UL Tx subframe and the A-UL Tx subframe donot temporally overlap with each other because they are forwardlyshifted.

If the B-UL Tx subframe is forwardly shifted by one symbol or more, abackhaul SRS can be transmitted over the first symbol other than a guardtime. In this case, the backhaul SRS can be aligned with the macro SRSof the M-UL Rx subframe by symbol unit, as shown in FIG. 36. Since themacro SRS and the backhaul SRS can be multiplexed and transmitted, acollision with a PUSCH and a PUCCH received through the M-UL Rx subframecan be avoided.

In order to increase the number of symbols which can transmit backhauluplink data over the B-UL Tx subframe through which the backhaul SRS istransmitted, the eNB may allow an Ma UE to always transmit data in ashortened format. For example, irrespective of whether a macro SRS hasbeen transmitted, the Ma UE can always transmit data in the shortenedformat. Alternatively, the eNB may inform the RN of a subframe throughwhich the Ma UE does not transmit the macro SRS and may configure thesubframe as a subframe using the shortened format. In this case, the RNmay take the amount of possible backhaul resources into account whendetermining whether the backhaul SRS is transmitted, the format of anR-PUSCH and the like. The utilization of resources can be increased bysharing information about macro SRS transmission timing and backhaul SRStransmission timing between the eNB and the RN.

FIGS. 37 and 38 illustrate the symbol indices of B-UL Tx subframes overwhich a backhaul SRS is transmitted.

As shown in FIGS. 37 and 38, the backhaul SRS can be transmitted overthe first symbol of a B-UL Tx subframe other than guard times. In thiscase, the symbol indices of the B-UL Tx subframe may be assigned foreach symbol (e.g., for an OFDM symbol or SC-FDMA symbol) in time periodsother than the guard times. In FIG. 37, the index of the first symbolthrough which the backhaul SRS is transmitted is assigned 12, andindices from 0 to 11 are sequentially assigned to subsequent symbols.According to the method of assigning symbol indices, it may be said thatthe backhaul SRS is always transmitted through the symbol 12 despite theposition of physical resources. In FIG. 38, the index of a first symbolthrough which a backhaul SRS is transmitted assigned 0, and indices from1 to 12 are sequentially assigned to subsequent symbols. If a backhaulSRS is transmitted, 13 symbols may be used in the B-UL Tx subframe. If abackhaul SRS is not transmitted, 12 symbols may be used in the B-UL Txsubframe.

FIG. 39 is a block diagram showing a source station and a destinationstation.

The source station 10 may be an eNB. The source station 10 includes aprocessor 11, memory 12, and a Radio Frequency (RF) unit 13. Theprocessor 11 implements the proposed functions, processes, and/ormethods. That is, the processor 11 can transmit a synchronization signalto the destination station and can transmit information for an offsettime and an additional timing adjustment command TA′. The layers of aradio interface protocol may be implemented by the processor 11. Thememory 12 is coupled to the processor 11 and configured to store variouspieces of information for driving the processor 11. The RF unit 13 iscoupled to the processor 11 and configured to transmit and/or receive aradio signal.

The destination station 20 may be a UE (i.e., an RN, an Ma UE, or an ReUE). The destination station 20 includes a processor 21, memory 22, andan RF unit 23. The processor 21 receives a synchronization signal,information for an offset time, and an additional timing adjustmentcommand and determines the timing of a subframe over which a signal istransmitted or received. The layers of a radio interface protocol may beimplemented by the processor 21. The memory 22 is coupled to theprocessor 21 and configured to store various pieces of information fordriving the processor 21. The RF unit 23 is coupled to the processor 21and configured to transmit and/or receive a radio signal.

The processor 11, 21 can include an Application-Specific IntegratedCircuit (ASIC), other chipset, a logic circuit, a data processor and/ora converter for converting a baseband signal and a radio signal, andvice versa. The memory 12, 22 may include Read-Only Memory (ROM), RandomAccess Memory (RAM), flash memory, a memory card, a storage mediumand/or other storage devices. The RF unit 13, 23 includes, one or moreantennas for transmitting and/or receiving a radio signal. When theembodiments are implemented in software, the above schemes may beimplemented using a module (process, function or the like) whichperforms the above functions. The module can be stored in the memory 12,22 and executed by the processor 11, 21. The memory 12, 22 may be placedinside or outside the processor 11, 21 and connected to the processor11, 21 through a variety of well-known means.

Although the some embodiments of the present invention have beendescribed above, a person having ordinary skill in the art willappreciate that the present invention may be modified and changed invarious ways without departing from the technical spirit and scope ofthe present invention. Accordingly, the present invention is not limitedto the embodiments and the present invention may be said to include allembodiments within the scope of the claims below.

What is claimed is:
 1. A method of transmitting a signal, performed by abase station, in a wireless communication system, the method comprising:transmitting a backhaul downlink signal to a relay station through abackhaul downlink transmission subframe, wherein the backhaul downlinktransmission subframe includes 14 orthogonal frequency divisionmultiplexing (OFDM) symbols and the 14 OFDM symbols are indexed 0 to 13,and wherein an access downlink transmission subframe, used by the relaystation to transmit a signal to a user equipment, and the backhauldownlink transmission subframe are transmitted with a time alignedsubframe boundary, and OFDM symbols having indices K to 12 are used fortransmitting the backhaul downlink signal, where K is a natural numberand 1≦K≦3.
 2. The method of claim 1, wherein both the access downlinktransmission subframe and the backhaul downlink transmission subframeinclude a first slot and a second slot in time domain.
 3. The method ofclaim 2, wherein both the first slot and the second slot include 7 OFDMsymbols in a normal cyclic prefix.
 4. The method of claim 1, wherein thebackhaul downlink signal is transmitted in a time period from an OFDMsymbol, having an index of 2 or 3 in the backhaul downlink transmissionsubframe, to an OFDM symbol having an index of 12 in the backhauldownlink transmission subframe.
 5. An apparatus for transmitting asignal in a wireless communication system, the apparatus comprising: aradio frequency unit configured to transmit and receive a radio signal;and a processor coupled to the radio frequency unit and configured totransmit a backhaul downlink signal to a relay station through abackhaul downlink transmission subframe, wherein the backhaul downlinktransmission subframe includes 14 orthogonal frequency divisionmultiplexing (OFDM) symbols and the 14 OFDM symbols are indexed 0 to 13,and wherein an access downlink transmission subframe, used by the relaystation to transmit a signal to a user equipment, and the backhauldownlink transmission subframe are transmitted with a time alignedsubframe boundary, and OFDM symbols having indices K to 12 are used fortransmitting the backhaul downlink signal, where K is a natural numberand 1≦K≦3.
 6. The apparatus of claim 5, wherein both the access downlinktransmission subframe and the backhaul downlink transmission subframeinclude a first slot and a second slot in time domain.
 7. The apparatusof claim 6, wherein both the first slot and the second slot include 7OFDM symbols in a normal cyclic prefix.
 8. The apparatus of claim 5,wherein the backhaul downlink signal is transmitted in a time periodfrom an OFDM symbol, having an index of 2 or 3 in the backhaul downlinktransmission subframe, to an OFDM symbol having an index of 12 in thebackhaul downlink transmission subframe.